Patent Application
20070095281
The present invention relates to power supplies, systems, and methods for chemical vapor deposition.
Chemical vapor deposition (CVD) is a process whereby a film is deposited on a substrate by reacting chemicals together in the gaseous or vapor phase to form a film. The gases or vapors utilized for CVD are gases or compounds that contain the element to be deposited and that may be induced to react with a substrate or other gas(es) to deposit a film. The CVD reaction may be thermally activated, plasma induced, plasma enhanced or activated by light in photon induced systems.
CVD is used extensively in the semiconductor industry to build up wafers. CVD can also be used for coating larger substrates such as glass and polycarbonate sheets. Plasma enhanced CVD (PECVD), for example, is one of the more promising technologies for creating large photovoltaic sheets and polycarbonate windows for automobiles.
To coat large substrate surface areas rapidly, a substrate carrier moves the substrate 135 through the vacuum chamber 105 at a steady rate. Other embodiments however, could include static coating. As the substrate 135 moves through the vacuum chamber 105, the disassociation should continue at a steady rate, and target molecules from the disassociated feed gas are theoretically deposited evenly on the substrate, thereby forming a uniform film on the substrate. But due to a variety of real-world factors, the films formed by this process are not always uniform. And often, efforts to compensate for these real-world factors damage the substrate by introducing too much heat or other stresses. Accordingly, an improved system and method are needed.
Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims.
One embodiment of the present invention is a system for depositing films on a substrate. This systems includes a vacuum chamber; a linear discharge tube housed inside the vacuum chamber; a magnetron configured to generate a VHF, microwave, or other high energy power signals that can be applied to the linear discharge tube; a power supply, which can include an electronic amplifier, configured to provide a power signal to the magnetron; and a pulse control connected to the power supply. The pulse control is configured to control the duty cycle of the plurality of pulses, the frequency of the plurality of pulses, and/or the contour shape of the plurality of pulse.
Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawing wherein:
As previously described, real-world factors act to limit the quality of films created by deposition systems, including linear microwave deposition systems. One of these limiting factors is an inability to create and maintain uniform plasmas around the linear discharge tube. Non-uniform plasmas result in non-uniform disassociation at certain points along the linear discharge tube, thereby causing non-homogenous deposition on certain portions of the substrate.
One system for addressing low plasma density near the center of the linear discharge tube 110 uses a split inner conductor. For example, two conductors are used inside the non-conductive tube. Another system, shown in
Linear discharge systems are generally driven by a power system, which can include DC supplies and/or amplifiers, coupled to a magnetron. Further enhancements to power-density uniformity and plasma uniformity along the linear discharge tube can be realized by controlling this power system. For example, plasma uniformity along the linear discharge tube can be changed by controlling the following properties of a DC signal generated by one type of power system, a DC power system: DC pulse duty cycles, pulse frequencies, and/or signal modulation. Signal modulation includes modulation of amplitude or pulse amplitude, frequency, pulse position, pulse width, duty cycle or simultaneous amplitude and any of the frequency types of modulation. Signal modulation is discussed in commonly owned and assigned attorney docket number (APPL-007/00US), entitled SYSTEM AND METHOD FOR MODULATION OF POWER AND POWER RELATED FUNCTIONS OF PECVD DISCHARGE SOURCES TO ACHIEVE NEW FILM PROPERTIES, which is incorporated herein by reference.
Each of these changes directly changes the microwave power signal being introduced into the inner conductor of the linear discharge tube. Changes to the microwave power signal change the plasma uniformity around the linear discharge tube. And in many cases, changes to the DC power system can be used to control the plasma properties to thereby increase the uniformity of a chemical make up of the film. These enhancements to the power supply can be applied to single antenna systems, multiple antenna systems, multiple antenna systems with shields, etc.
Even further enhancements to a deposition system can be realized by contouring the power density in the linear discharge tube. The power density can be contoured by contouring the power signal being introduced into the inner conductor. One method of contouring the power signal being introduced into the inner conductor involves contouring the output of the DC power system. For example, the individual pulses of the DC power system can be contoured.
Particularly good results are anticipated when the degrading-pulse contours shown in
Referring now to
Recall that most linear discharge deposition systems include several linear discharge tubes. In certain instances, it may be desirable to offset the timing of the pulses driving adjacent linear discharge tubes. The microwaves generated by one linear discharge tube can travel to adjacent linear discharge tubes and impact power density and plasma uniformity. With proper timing control, that impact can be positive and can assist with maintaining a uniform power density and plasma. The timing control 185 can provide this timing control. These of skill in the art would understand how to tune the timing control.
The timing control 185 can also be used with linear discharge systems that include multiple magnetrons 170 and/or DC sources 160. In these systems, each linear discharge tube is driven by a separate magnetron and possibly a separate DC source. The timing control can be applied to each magnetron and/or each DC source. The terms “DC source” and “DC power supply” refer to any type of power system, including those that use a linear amplifier, a non-linear amplifier, or no amplifier. The terms can also refer to an amplifier by itself.
In conclusion, the present invention provides, among other things, a system and method for controlling deposition onto substrates. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.
